The soundscapes of the Anthropocene ocean are fundamentally different from those of pre-industrial times, becoming more and more a raucous cacophony as the noise from human activity has grown louder and more prevalent. In a Review, Carlos Duarte and colleagues show how the rapidly changing soundscape of modern oceans impacts marine life worldwide. According to the authors, mitigating these impacts is key to achieving a healthier ocean. From the plangent songs of cetaceans to grinding arctic sea ice, the world's oceans' natural chorus is performed by a vast ensemble of geological (geophony) and biological (biophony) sounds. However, for more than a century, sounds from human activities on the high seas, like fishing, shipping and development, have increasingly added to the mix, making modern oceans far noisier than ever before. But it's not just new noises added - human activities have also made some areas of the ocean quieter. For example, the deterioration of habitats like coral reefs and the hunting of large marine mammals, including highly vocal whales, has led to drastic declines in the abundance of sound-producing animals. As well, the loss of sea ice due to our rapidly warming climate has drastically altered the natural acoustics of Arctic marine environments. By evaluating more than 40 years' worth of published research, Duarte et al. find that anthropogenic noise, or "anthrophony," - a third component on top of biophony and geophony - is negatively impacting marine animals, affecting their behavior, physiology and, in some cases, their overall survivability. However, unlike many other anthropogenic stressors on marine ecosystems, the authors argue that the harmful effects of noise pollution could rapidly decline through the mitigation and regulation of sources of marine noise. "Changing ocean soundscapes have become the neglected 'elephant in the room' of global ocean change," write Duarte et al. "In an era when societies increasingly look to the 'blue economy' as a source of resources and wealth, it is essential that ocean soundscapes be responsibly managed to ensure the sustainable use of the ocean."